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An ignition interlock device is a handheld breathalyzer that is installed directly into your vehicle. The devices come in different shapes and sizes but are usually about the size of a television remote.

The first ignition interlock device hit the market in 1988 and after proving to be successful in preventing drunk driving fatalities, their use nationwide has increased each year.

An ignition interlock device is comprised of a few different pieces:

  • Handheld unit
  • Mouthpiece
  • Relay cord connecting the device to your vehicle
  • Camera unit (if required to have by your state)

There are numerous ignition interlock device manufacturers in the United States and each device looks a little different but ultimately, they all have the same components and are roughly the same size.

The handheld fits comfortably in your center console and the relay cord is long enough to allow you to move the device around your front seat, as needed. The camera (if required), is mounted to the front windshield by an official installer.

Now that you’ve had a brief introduction to what an ignition interlock device actually is, let’s dive deeper into how it works.

How does an ignition interlock work?

Ignition interlock devices have two main jobs:
1) Prevent somebody from starting their car while intoxicated
2) Guarantee continued sobriety from the driver throughout their time behind the wheel

Let’s look at how the devices work to accomplish each of these goals.

Preventing a driver from starting the vehicle while intoxicated

Anybody with an ignition interlock device installed in their vehicle will be required to provide a breath sample into the mouthpiece of the device before they are able to start their vehicle.

State certified ignition interlock devices use a fuel cell technology to measure the amount of alcohol on the user’s breath. If the breath sample detects alcohol at or above the limit set by the state (usually 0.02), the car will not start.

If the breath sample returns a breath alcohol concentration (BrAC) below that set limit, the driver will be able to insert their key into the ignition and start their vehicle.

Each state has individual ignition interlock device laws and regulations that determine what happens if you provide a failing breath sample.

Some states allow you to try again after waiting a short period of time but may lock you out after so many failed samples. More about lockouts later on in the guide.

Other states allow you to continue blowing into the device until you’ve provided a passing breath sample and can start your car.

Your ignition interlock provider, attorney, court or Motor Vehicle Department can walk you through the requirements in your state so there aren’t any surprises.

Of course, the best way to get through an interlock requirement is to refrain from trying to drive after consuming any alcohol.

Continuous sobriety while the vehicle is running

Once your vehicle is started, an ignition interlock device will require you to continue providing breath samples throughout the duration of your trip.

Simply put, this ensures that the driver doesn’t just have a sober person start their vehicle for them so they could continue driving after drinking.

These continued tests, often referred to as random retests, are required by your state and all ignition interlock providers must abide by state laws requiring them.

Most ignition interlock providers give the driver 4-6 minutes to complete a retest once prompted. This allows the driver to pull over to the side of the road if needed or take extra precautionary measures if driving in heavy traffic.

Are retests safe?

Retests have proven to be safe and effective at separating drinking from driving and if done safely, can be executed without any issues. Your device will beep when a retest is required. At this time, you’ll simply provide a breath sample into the mouthpiece and can continue driving.

If you provide a breath sample with a BrAC above the limit set by your state, your vehicle will signal you to pull over and turn your car off. As with most things related to ignition interlock devices, the specifics differ by state.

Some states will require your horn to beep or your lights to flash after a failed retest until you turn your vehicle off. In NO situation will the ignition interlock device be able to actually turn your car off, though. Once your vehicle has been started, no ignition interlock device is able to turn it off.

What else might an ignition interlock device be called?
Ignition interlock device is the industry standard term, but like all other products, there are variations around what the mechanism is called. Often the devices are referred to as "car breathalyzers."That makes sense in literal terms as an ignition interlock device is, by definition, a breathalyzer for your vehicle.

You may also see "ignition interlock device" simply abbreviated as "IID." This will often appear on paperwork and court order requiring you to install one of the devices.

If your device isn't being referred to as ignition interlock device, an IID or a car breathalyzer, it may be called a "breath alcohol ignition interlock device" or "BAID". This terminology is primarily used in the state of Illinois but does appear in other states.

There are a number of home grown terms out there describing ignition interlock devices, like "blow 'n' go", but most often, you'll see it referenced as one of the classic names above.

Who needs an ignition interlock?
Since California became the first state to pass an ignition interlock law in 1988, interlocks quickly became established as the most effective way to prevent repeat drunk driving offenses.
License suspensions, the alternate to ignition interlock devices, are difficult to enforce and prove to be ineffective, as three out of four people with suspended licenses continue to drive, according to Mothers Against Drunk Driving (MADD).

Read more about the penalties for driving with a suspended license in your state.

Currently, 30 states, plus Washington D.C., require ignition interlock devices for all drunk driving offenders. States such as West Virginia, Arizona, Louisiana and New Mexico have seen drastic decreases in the number of alcohol related traffic fatalities after implementing all offender ignition interlock laws.

All offender states


National organizations, like MADD and National Highway Traffic Safety Administration (NHTSA) publicly support ignition interlock devices and push for their implementation for all drunk driving offenders.

According to MADD, ignition interlock devices have prevented over 2.3 million attempts to start a vehicle while intoxicated. As a result, thousands of lives have been saved because of ignition interlock devices.

Voluntary ignition interlock installation

Most ignition interlock device providers have a voluntary program at a discounted monthly rate. This allows people to install ignition interlock devices as a preventative measure and not only when ordered to as a result of a drunk driving conviction (DUI/OW/OUI/DWI).

Voluntary ignition interlock devices could be helpful in a number of situations:

  • To prevent drunk driving in a teen or young driver
  • To prevent repeat offenses, even if an interlock isn't installed
  • To prevent a first-time offense in a friend or family member
  • To continue with your interlock even after you've fulfilled your required time
  • To guarantee sobriety for drivers of a company vehicle